d3d11device: Add an optional flags argument for creating device

Extend gst_d3d11_device_new() method so that caller can specify D3D11_CREATE_DEVICE_FLAG value to use.

See https://docs.microsoft.com/en-us/windows/win32/api/d3d11/ne-d3d11-d3d11_create_device_flag for more detail about D3D11_CREATE_DEVICE_FLAG